Retargeting is hot and getting hotter. Witness relatively new startup AdRoll claiming revenue increases of over 400% together with over 2,000 new advertising clients. In support, trends-tracking company BuiltWith lists AdRoll’s technology as the "fastest growing advertising technology" with ad network ExoClick close behind.

In fact, according to W3Techs: AdRoll is the fastest growing advertising network at the moment, increasing more than threefold in 2011.

Look to see more retargeting in the performance marketing space. It will be an important differentiator within a very short space of time.